This invention relates generally to window wipers and more specifically to a window wiper system for an automotive vehicle.
It is common in the automotive industry to employ windshield and rear window wiper systems that have an electric motor and a worm gear which are constantly reversing direction in order to oscillate a wiper arm and wiper blade back and forth within a wiping range or path on the window. In other words, the electric motor and worm gear rotate in first respective directions for moving the wiper arm and blade to one side of the window and then reverse directions for moving the wiper arm and blade to the other side of the window. In some situations, the electric motor and worm gear are further rotated to move the wiper arm and blade off of the window to a park position.
These constantly reversing electric motors often suffer from objectionable noise and are prone to a shortened duration due to the longitudinal impact of the ends of the armature shaft against the adjacent bearing and end plug members retaining the armature shaft. These conventional devices also cause a high stress enmeshed condition between the worm gear portion of the armature shaft and the driven worm gear teeth thereby causing gear tooth breakage.
It is also known to provide a four-bar linkage to couple a worm gear to a window wiper shaft. In this arrangement, an electric motor and worm gear rotate in a unidirectional manner to facilitate back and forth oscillation of a window wiper arm and blade. In this unidirectional, four-bar linkage construction, a pin always moves concurrently with the worm gear, since the pin is always fixed to the worm gear in a single location. The pin is also coupled to the four-bar linkage. This serves to reduce noise and encourage prolonged life of the electric motor and gears, but has proven difficult to provide a wiper arm and wiper blade park position off of the window. Moreover, the four-bar linkage cannot remain stationary if the worm gear is rotated. Such an arrangement is disclosed in U.S. Pat. No. 5,182,957 entitled "Drive Unit, in Particular for a Windshield Wiper System on a Motor Vehicle" which issued to Bohmer et al. on Feb. 2, 1993.
It is also known to provide a window wiper construction having an electric motor and a worm gear with a continuous and closed loop cam track. A pin connected to a drive pawl rides in the cam track. In one position, the pin of the drive pawl is cammed from engagement with a shoulder of the cam track so as to interrupt the driving connection between an output shaft coupled to the wiper and the worm gear. Such an arrangement is disclosed in U.S. Pat. No. 3,688,332 entitled "Mechanism for Opening and Closing a Cover for a Concealed Wiper System" which issued to Bellware on Sep. 5, 1972. Notwithstanding, this device appears to be overly complex. It also requires a large number of parts which adds undue expense. Moreover, disengagement of the drive pawl from the cam track can cause reengagement difficulties due to tolerance mismatches of parts or due to operation of the device on a bumpy road.